This invention relates to a liquid compost aerator and, more particularly, to a liquid compost aerator utilising a vortex generator to create small bubbles used in the aerating action and to the method used in operating the vortex generator for aerobic bacterial breakdown.
The use of bubbles for assisting in the aeration of a liquid compost waste solution is well known. Such a process used in the liquid composting process is called aerobic, and utilises oxygen in breaking down sewage and like materials. This is as opposed to the non-oxygen or anaerobic process of bacterial breakdown. The use of aeration in bacterial breakdown enhances the breakdown action and has other advantages. Following the bacterial breakdown of the waste material into components, some of such components may be used as fertilizer which otherwise can be expensive. Thus, bacterial breakdown of waste materials can be attractive.
The aeration action using bubbles typically uses a bubble generator. Water or other liquid is mixed with the compost and bubbles are generated beneath the surface of the liquid. These bubbles rise to the surface and, in doing so, distribute air within the compost-liquid mix. The air aerates the mix and assists in the bacterial breakdown.
U.S. Pat. No. 3,778,233 (Blough et al), for example, discloses an elongated hollow shaft with a propeller secured to one end, which propeller is immersed in the liquid waste material. The operation of the propeller induces bubbles and movement within the waste material which enhances the aerobic process. A further example of a propeller system is described and illustrated in U.S. Pat. No. 4,240,990 (Inhofer et al).
The bubbles generated by the apparatuses of the above-identified and other known prior art are generated by propeller action. That is, propellers are immersed in the compost-liquid mix and revolved, often at relatively high speeds. The revolving action of the propellers causes turbulence within the mixture and the concomitant generation of bubbles. The bubbles assist in dispersing oxygen throughout the mixture which, as discussed, enhances the efficacy of the aeration action in breaking down the compost.
It is important in the aeration action to generate bubbles that are relatively small. The smaller the bubbles, the more numerous they will be and the total surface area of the air bubbles will be greater. The greater surface area of the bubbles will result in more air being dispersed throughout the compost/liquid mix. The smaller bubbles will rise more slowly to the surface and will therefore be dispersed more uniformly throughout the mix and over a greater area.
Propellers generate bubbles that are relatively large, even at high speeds of revolution. And, of course, the relatively large diameter of the propellers used for bubble generation does limit the speed of rotation. While the relatively large bubbles do cause aerobic action, the bubbles rise to the surface quickly and are not, therefore, dispersed widely throughout the compost/liquid mixture.
According to one aspect of the invention, there is provided air entrainment apparatus to entrain air in liquid comprising a liquid inlet for supplying liquid to a liquid conveying channel, an air inlet to allow the entry of air to said liquid conveying channel, said air being introduced into said liquid in said liquid conveying channel and a vortex generator downstream from said point of introduction of said air and said liquid to said liquid conveying channel, said vortex generator being operable to cause turbulence in said liquid conveying channel and to create bubbles in said liquid, said liquid forming an annular portion within said liquid conveying channel adjacent to said vortex generator.
According to a further aspect of the invention, there is disclosed a method of creating turbulence in a liquid/air mixture for aerobic bacteria breakdown comprising the steps of conveying liquid through a liquid carrying channel, allowing air to enter said liquid in said liquid carrying channel from an air inlet, reducing the cross-sectional area of said liquid carrying channel by positioning a vortex generator having a skirt with a diameter increasing from an upstream to a downstream position and allowing said liquid carrying channel to increase in cross-sectional area immediately downstream of the widest diameter of said skirt of said vortex generator.